Boot KVM guests via UEFI by default; per-image firmware setting

Run 5 on the real host bisected the guest hang: the Debian 13 image
hangs after GRUB under SeaBIOS with or without our seed and with either
CPU model, and boots under OVMF. The image's legacy boot chain is the
problem, not the provider.

images.<key>.firmware is "uefi" (default) or "bios". The domain XML
emits <os firmware="efi"> with secure boot off, so libvirt selects the
OVMF binary and manages the NVRAM file, which the existing nvram undefine
flag removes. Direct-URL images default to UEFI too. OVMF joins the
hypervisor prerequisites; sample, config table, known gaps, decision log
and the execution log record the finding.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
This commit is contained in:
2026-09-10 19:13:51 +00:00
co-authored by Claude Fable 5.1
parent 5a6c889531
commit 9a393b1df8
12 changed files with 151 additions and 26 deletions
@@ -477,3 +477,40 @@ outside the operator). Because the provider's own logs were invisible in
the test output, this run also produced a side plan:
[2026-09-10-0805-kvm-libvirt-tracing](2026-09-10-0805-kvm-libvirt-tracing.md),
which traces every libvirt RPC at V(1) and routes it into `-v` output.
### Run 5: the guest hang is Debian 13's BIOS boot path; UEFI fixes it
The cached image's sha512 matched Debian's published sum, and
`qemu-img info` showed a sound 3 GiB qcow2, which also confirms that
the raw upload over a libvirt-created volume plus pool refresh yields a
byte-identical file (the Step 3b note is answered). Bisected by hand on
beelink with `virt-install --import` on a fresh overlay of the same
image:
| variant | seed | CPU | firmware | result |
|---|---|---|---|---|
| operator's domain | ours | host-passthrough | SeaBIOS | hangs after GRUB "Booting", 100 % CPU |
| bare | none | host-passthrough | SeaBIOS | same hang |
| bare | none | host-model | SeaBIOS | same hang |
| bare | none | host-passthrough | **OVMF (`--boot uefi`)** | **boots to login** |
So neither the seed ISO, the domain XML nor the CPU model was the
problem: the image's legacy GRUB → kernel handoff does not work on this
host, while its EFI stub path does. Not diagnosed further; it is
Debian's chain, not ours, and every current cloud image boots UEFI.
Change: `images.<key>.firmware` (`uefi` default, `bios` escape),
threaded through `withDefaults` → `imageSource` → `domainParams`, and
`buildDomainXML` emits `<os firmware="efi"><firmware><feature
enabled="no" name="secure-boot"/></firmware>` so libvirt selects the
OVMF binary and creates the NVRAM file; the `nvram` undefine flag Delete
already passes removes it (seen on the host: `virsh undefine` without
`--nvram` refuses such a domain). Direct-URL images default to UEFI
too. Docs: OVMF is a new hypervisor prerequisite, config table row,
sample comment, known-gaps entry, decision-log entry.
Worth noting: the first image download went through with no checksum
configured, and the cache reuses a base image by key, so switching
`KVM_TEST_IMAGE_URL` requires deleting `base-test-image.qcow2` and its
marker by hand first. That is the reviewer's Step 4 finding showing up
in practice; still documented rather than fixed.